Raid 1 volume will not expand to fill disk space

I have a Raid 1 volume using 2 3T drives. I replaced drive 1 with a 6T drive and rebuilt the Raid. I then replaced the second drive with a 6T drive and rebuilt the Raid. With both 6T drives in place I had the system expand the Raid. The system prompted that it was expanding the Raid as expected. It ran all night plus several. Unfortunately, when it was complete, it was NOT expanded. It was the same size as before (2.94T).

What do I need to do to get the raid to use the entire disk space available?

I contacted tech support. Their reply was that a RAID 1 can not be expanded. I will have to move the information off, create the new RAID 1 volume, and then move the information back.

Indeed; unlike RAID 5, RAID 1 is not normally a RAID level designed for expansion.